In the advanced chip packaging methods, the WLCSP (Wafer Level Chip Scale Packaging) technique is a technique in which packaging and tests are performed on a semiconductor wafer and then the wafer is molded and singulated into individual IC packages. The IC package size after packaging is almost the same as the original size of the bare die. The package has good heat dissipation and electrical properties.
Usually, the thickness of the semiconductor chip is reduced to a certain value based on the requirement of substrate resistance reduction or chip size reduction. However, the thinner the chip is, the more easily it cracks. Therefore, any shape modification of the semiconductor chip should be avoided. However, the actual fabrication processes have some issues, for example, singulation of the wafer easily causes the edge or corner of a chip to crack resulting in the chip being fragile or lacking the corner. On the other hand, in most of the current wafer level chip scale packages some parts of the chip in the devices are exposed from the molding compound, which results in poor moisture resistance and lacks of mechanical protection that causes damage in its electrical properties.
U.S. Patent Application Publication No. 2009/0032871 discloses a WLCSP method of forming a semiconductor device including some electrodes on the front side of the semiconductor chip connected with those on the backside of the chip by a conductive structure positioned to an edge of the chip, with the electrodes on the backside of the chip exposed out of the molding compound after the chip is molded and separated from the wafer.
U.S. Pat. No. 6,107,164 also discloses a WLCSP method of manufacturing a semiconductor device. In this method, the protruded electrodes are formed on a plurality of chip areas on a front side of a wafer. Grooves are defined in boundary regions of the plurality of the chip areas. The surface of the wafer with the grooves is covered with a molding compound. Thus, the wafer is thinned on its backside to expose the grooves. The individual chips are separated from the wafer by cutting at the exposed groove portions with the backside of the resulted chip exposed out from the molding compound.
Furthermore, U.S. Pat. Nos. 6,420,244 and 6,852,607 also disclose similar WLCSP methods.
However, the conventional WLCSP methods have not disclose a method for completely seal the chip for protection while reducing the thickness of the wafer and to maintain a certain thickness of the thinned wafer to provide mechanical support sufficient for subsequent working procedures.